1. Field
The present invention relates to an electric vehicle, such as an in-wheel motor vehicle, that is equipped with motor(s) to drive wheels and that may be battery-powered or fuel cell-powered.
2. Description of the Related Art
An electric vehicle may experience degradation in performance or malfunctions of a motor serving as a drive for the vehicle. This can significantly affect the travel performance or travel safety. A battery-powered electric vehicle may include a drive system. The drive system may employ an IPM (e.g., Interior Permanent Magnet synchronous motor). Such an IPM may include a neodymium magnet to provide a highly efficient performance, thus increasing the maximum travel range that is possible with a limited battery capacity.
An electric vehicle can typically include a synchronous motor or an induction motor that may be driven with an AC current converted by an inverter from a DC current supplied from a battery. The inverter, which can, in principle, include a plurality of semiconductor switching devices, may conduct a large current to drive the motor, thus generating a significant heat. The characteristics of semiconductor switching devices may considerably vary with temperature. Overheat may even damage the semiconductor switching devices. In order to address these, an inverter is typically equipped with a cooling system.
In the past, an in-wheel motor drive system has been proposed in which, to ensure reliability, the temperature of components such as a wheel bearing, a reducer and a motor may be measured and monitored for overload, with features to limit a drive current in/to the motor or a rotational frequency of the motor according to the temperature measurements. For example, see Japanese Patent Publication No. 2008-168790